The banks where I live use one time pads for authentication, which makes it impossible for Mint to work.
Which country?
Finland
In Germany it seems common to mail lists of transaction authentication numbers to customers, and in the Netherlands smart card readers that read your card and generate a TAN seem standard. There are companies built around circumventing this and allowing third parties access to your account (sofortueberweisung.de, for example), but it usually is against the bank EULA.